The lamps or bulbs for retrofit applications are enjoying a growing popularity as possible replacements of halogen sources in motor vehicle headlamps, e.g. in the aftermarket business.
Various lamps or bulbs employ LED sources as light radiation sources. This is due to the consolidation of SSL (Solid State Lighting) technology and to the advantages inherent in LED light radiation sources, e.g. a long service life, low power absorption, the different Correlated Colour Temperatures (CCTs), leading e.g. to the achievement of a cooler white light than the light emitted by halogen bulbs.
The lamps for the automotive sector (such as e.g. the headlamps of a motor vehicle) may include photometrical functions that are particularly important for the safety of the driver and of other road users. The international organizations have therefore defined the characteristics which must be present in the beam emitted by such lamps, e.g. in terms of shape and luminous intensity.
One of the purposes of the developers of such lamps is to design the optical system (e.g. a reflector in the case of traditional halogen light sources) adapted to project the image of the bulb filament towards the road. The size and the position of the filament and the flux emitted by the lamp or bulb are crucial parameters in the design of the reflector, e.g. for low beam and high beam headlamps. Small variations of these parameters are adapted to affect the lamp functionality, possibly leading to a failure to comply with the specifications defined in the international regulations.
However, the introduction of LED light radiation sources for lamps or bulbs, e.g. for retrofit applications, involves difficulties in reproducing the emission, e.g. the light emitting volume, of a traditional filament.
Presently, the most common retrofit lamps or bulbs based on LED sources may include an array of two or more LEDs arranged on two substrates (e.g. Printed Circuit Boards, PCB), which are assembled with the planar faces parallel to each other, so as to facilitate the emission of the LED light radiation in opposite directions.
This layout, however, may not ensure that the lamp (e.g. a high beam/low beam headlamp) is compliant with regulations, e.g. because the achievable light emitting volume fails to reproduce the light emitting volume of a traditional filament, and therefore the light is emitted with a radiation pattern which is not symmetrical around the bulb axis.
Document WO 2016/158542 A1 describes a light source facing a lens, as well as a reflector having cylindrical symmetry around an optical axis. The lens changes the direction of the light from the light source, and deflects the beam towards the reflector.
Document US 2016/0010829 A1 describes an optical arrangement including a cup-shaped reflector, a light source and a lens facing the source, the reflector and the light being formed together.
Document US 2016/0215959 A1, which claims the priority of German Application DE 10 2015 201 300.6, describes a lighting device including a light source, an ellipsoidal reflector, an aspheric lens and an exit pupil as output of the lighting device. The aspheric lens is arranged between the ellipsoidal reflector and the exit pupil, and it is shaped in such a way that a part of the reflected light passes through the lens with an aperture angle not wider than 5°. Another part of the reflected light enters the aspheric lens in an outer region, and is driven towards the emission pupil.
Document FR 2 799 269 A describes a method for modifying the light distribution of a source the image whereof is projected by a lens passing through a light transmitting element, including a plurality of plates.
Document US 2015/0247615 A1 describes an extruded optical system for a UV device, wherein the light emitted by a rod-shaped, solid-state light radiation source is collected by an elongated elliptical reflective mirror and is condensed by a lens acting as output element.
Document US 2006/0028834 A1 describes a projection system including a light source, an ellipsoidal reflector, an elongated transparent glass rod and a collimating lens, spaced in the distal direction from the end of the rod. All the components of the optical system are coaxial with the optical axis.
Document US 2015/036357 A1 describes a reflector assembly for eliminating stray light and including a reflector, having a focal point whereat a light source is arranged, and a facing lens configured to reflect the rays backwards with respect to the light source.
Document GB 2 489 384 A describes a rod having light reflecting properties and arranged on a shaft. The outer surface of the rod is irregular and includes a plurality of faces having a variety of different shapes and sizes. The reflective surfaces are formed by a coating of light reflective material.
Document WO 03/060580 A1 describes a lighting device including a light transparent rod, having a light source located at one end of the rod, with a linear reflector extending longitudinally of the rod.
The Italian Patent Application 102016000059954 (corresponding to the U.S. patent application Ser. No. 15/250,988) describes a lighting device including a solid-state source and a light permeable body, which collimates and directs the light towards a distal portion including a mirror, so as to emulate the emission of a filament.